From: Tom Lane <tgl@sss.pgh.pa.us>
To: Mark Dilger <mark.dilger@enterprisedb.com>
cc: Peter Eisentraut <peter.eisentraut@2ndquadrant.com>,
        =?utf-8?Q?Juan_Jos=C3=A9_Santamar=C3=ADa_Flecha?=
 <juanjo.santamaria@gmail.com>,
        Alvaro Herrera <alvherre@2ndquadrant.com>,
        Arthur Zakirov <zaartur@gmail.com>,
        Tomas Vondra <tomas.vondra@2ndquadrant.com>,
        PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>
Subject: Re: Allow to_date() and to_timestamp() to accept localized names
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Comments: In-reply-to Mark Dilger <mark.dilger@enterprisedb.com>
	message dated "Tue, 28 Jan 2020 11:05:09 -0800"
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Date: Tue, 28 Jan 2020 14:37:50 -0500
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Mark Dilger <mark.dilger@enterprisedb.com> writes:
>> On Jan 28, 2020, at 9:30 AM, Tom Lane <tgl@sss.pgh.pa.us> wrote:
>> A brute-force answer, if there are few enough cases, is to recognize
>> them regardless of the specific value of LC_TIME.  Do we think
>> anybody would notice or care if to_date('Sonnabend', 'TMDay') works
>> even when in a non-German locale?

> I think this only becomes a problem if there are weekday or month name c=
ollisions between languages where they have different meanings.  As an abs=
urd hypothetical, if =E2=80=9CSunday=E2=80=9D in Tagalog means what =E2=80=
=9CTuesday=E2=80=9D means in English, then you=E2=80=99ve got a problem.

> This does happen for month abbreviations.  =E2=80=9CMar=E2=80=9D is shor=
t for =E2=80=9CMarch=E2=80=9D and variations in a number of languages, but=
 short for =E2=80=9CNovember=E2=80=9D in Finnish.

> For day abbreviations, =E2=80=9CSu=E2=80=9D collides between fi_FI and h=
r_HR, and =E2=80=9Ctor=E2=80=9D collides between sl_SL and no_NO.

But none of those cases are alternative names, so we wouldn't have
entries for them in this hypothetical list.  They'd only be recognized
when strftime() returns them.  I suspect also that the abbreviated
names have few if any alternatives, so we may only need this whole hack
for full names.

A possible way of tightening things up without explicitly decoding the
locale name is to make the entries of the list be string pairs: "if
strftime() returned this, then also consider that".  That puts a bit
of a premium on knowing which names strftime considers primary, but
I think we'd have had to know that anyway.

			regards, tom lane